Guarding against Dickeya: testing your seed potatoes

After triggering major crop losses in the United States, Dickeya has been dominating the potato meetings circuit in North America for the past year or two.

In Canada, some of the discussions revolve around the consequences for growers should the new disease makes its way into this country — but some industry experts maintain Dickeya is likely already here.

Gary Secor, professor of plant pathology at North Dakota State University (NDSU):
 

“I don’t know what the extent is [in Canada], but we found Dickeya in samples that were sent to us from Ontario and from New Brunswick.”

“I think that certainly the potential is there for Dickeya to be present and I think the Canadian farmer should be aware of that and take it seriously.”

Researchers in the Plant Pathology department at NDSU, along with six labs in the U.S. and Canada, has been conducting research into Dickeya testing as part of an initiative to develop better and more standardized methods for diagnosing the disease.

Led by Amy Charkowski, head of Colorado State University’s Bioagricultural Sciences and Pest Management department, the collection of researchers also includes Mathuresh Singh, director of Potato New Brunswick’s Agricultural Certification Services Inc. (ACS) lab in Fredericton, New Brunswick. Both Charkowski and Singh spoke to Canadian growers about Dickeya at Manitoba Potato Production Days in Brandon, Manitoba, in January.

Because Dickeya spreads primarily through infected seed, testing potato seed lots for the pathogen (or adding Dickeya to wider disease screening) is becoming an increasingly popular choice for potato seed growers and buyers in the United States.

Dickeya testing is also on the rise in Canada. A&L Canada Laboratories in London, Ontario has been offering Dickeya testing since 2015, and company officials say more and more customers are requesting the service as a way to ensure no Dickeya-infested seed is planted in their potato fields.

The ACS lab in New Brunswick started Dickeya testing in mid-2016. Singh says it’s because most of New Brunswick’s seed potatoes are sold in Maine and other states along the Eastern Seaboard of the United States, and some of those buyers are now asking for Dickeya screening.

Mathuresh Singh, director of Potato New Brunswick’s Agricultural Certification Services Inc. (ACS):
 

“Our lab is owned by the potato growers of New Brunswick and we offer any services they need, so that’s why we got involved in the Dickeya testing — not because we had a problem here but just because there’s a demand for this”

Origins of Outbreak

Dickeya is one of a number of bacterial pathogens that can cause blackleg in potatoes. Capable of spreading over long distances through infected plant material that can include other vegetables and some ornamental plants, Dickeya species have been affecting potatoes in Europe since the 1970s. Three different genotypes of the disease have been found in the US but most of it is Dickeya dianthicola.

Experts agree that prior to the D. dianthicola outbreak in the US in 2015, the pathogen was probably present in seed potatoes and farms in affected states for several years. It is believed rains in 2013 and 2014 likely helped spread the disease, but symptoms were held in check by cooler weather; Dickeya symptoms typically develop when temperatures exceed 25 C.

Warmer temperatures in 2015 resulted in a major outbreak on commercial farms in Maine, which then spread to other states along the Eastern Seaboard and in the Midwest. According to Secor and Charkowski, Dickeya has now been confirmed in 20 U.S. states.